Novel acrylonitrile polymer fibers and process for producing the same

ABSTRACT

A ACRYLIC FIBER IS PROVIDED WITH PROTUBERANCES OF MORE THAN 0.2U HEIGHT AT INTERVALS IN THE RANGE OF 1.5 TO 12U ON THE PERIPHERAL SURFACE THEREOF. THIS NOVEL ACRYLIC FIBER IS MANUFACTURED BY TREATING THE FIBER WITH A DENATURALIZING AGENT SUCH AS ALKALI METAL HYDROXIDES, SULFURIC ACID, HYDROXYLAMINE SALTS, AND HYDRAZINE, AND IMMERSING THE TREATED FIBER INTO A SHRINKING AGENT SUCH AS GLYCOLS HYDROTROPIC AGENTS, METALS HAVING A LOW MELTING POINT AND ORGANIC CARBONATE OR Y-BUTYROLACTONE SOLUTIONS WHICH CAN DISSOLVE THE ACRYLONTRILE POLYMER.   D R A W I N G

Apn] 17, 1973 ZEN-ICHI ORITO ET AL 3,728,072

NOVEL ACRYLONITRILE POLYMER FIBERS AND PROCESS FOR PRODUCING THE SAME Filed July 23, 1969 2 Sheets-Sheet 1 April 17, 1973 cm o n-o ET AL 3,728,072

NOVLL ACRYLONITRILE POLYMER FIBERS AND PROCESS FOR PRODUCING THE SAME Filed July 23, 1.969 2 Sheets-Sheet 2 7 FRICTIONAL FORCE PULL OUT RESISTANCE -r\nuu u ow\loow o 2 4 6 8 IO PULL OUT DISTANCE (cm) GRADE) HAND INTERVAL OF PROTUBERANCE (p) United States Patent Office 3,728,072 NOVEL ACRYLONITRILE POLYMER FIBERS AND PROCESS FOR PRODUCING THE SAME Zen-Ichi Orito, Hiroshi Sugimoto, Minoru Uchida, Hajime Sahara, Masatoshi Takesue, and Kiyoharu Nishida, Nagoya-shi, Aichi-ken, Japan, assignors to Mitsubishi Rayon Company Limited, Tokyo, Japan Filed July 23, 1969, Ser. No. 844,105 Claims priority, application Japan, July 31, 1968, 43/5 3,103; Nov. 29, 1968, 43/87,438 Int. Cl. D02g 3/02, 3/24; D06m 3/18 US. Cl. 8115.5 8 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to a novel and improved acrylonitrile polymer fiber having protuberances on the surface of the fiber and a process for producing the fiber. More particularly, the present invention relates to a novel acrylonitrile polymer fiber having differential frictional effect due to the protuberances on the surface of the fiber and a process for producing the fiber.

\Vhile acrylonitrile polymer fiber has been used widely in the field of knitted or woven fabrics due to its good physical properties, the fiber is not favoured by some customers due to its different hand feel from that of natural fiber. Accordingly, many efforts have been made to produce a hand feel of acrylonitrile polymer fiber similar to that of natural fiber but these efforts have been without complete success. That is, attempts have been made to give a wool-like hand feel to acrylonitrile polymer fiber by improving its crimp characteristics through conjugate spinning or other methods. However, it has been found that it is impossible to obtain acrylonitrile polymer fiber having the highly resilient, soft and Wool-like oily hand feel, which is characteristic of wool fiber, by only improving its crimp characteristics.

Good quality wool fiber has protuberances on the fiber surface, so-called serration, affecting fiber processing and relating to hand feel of the fiber product, while conventional acrylonitrile polymer fiber has no such protuberances.

Accordingly, it is necessary to produce acrylonitrile polymer fiber having a surface similar to that of wool for obtaining an acrylonitrile polymer fiber product having a hand feel such as that of wool fiber products.

An object of the present invention is to provide a novel acrylonitrile polymer fiber having a special configuration and a process for producing the fiber. A further object of the present invention is to provide an acrylonitrile polymer fiber having differential frictional effect and a process for producing the fiber. A still further object of the present invention is to provide a novel acrylonitrile polymer fiber having a hand feel similar to that of good quality wool fiber and a process for producing such a fiber.

These objects are accomplished by making the outer layer of the fiber insoluble in dimethyl formamide at 75 C. and forming protuberances of more than 0.2a height at intervals along the fiber axis in the range of from 1.5 to 12 over the surface of the fiber.

3,728,072 Patented Apr. 17, 1973 'In the present invention, the cross-section of the protuberances along the fiber axis may be symmetrical or asymmetrical across the center line of the protuberances. The protuberances may run discontinuously around the fiber in such a state that an edge line of the protuberances is at an angle of from to to the fiber axis. The term discontinuously as used herein is intended to indicate that a majority of the protuberances do not make a complete, closed circle around the circumference of the fiber. In the present invention, the cross section is preferably asymmetrical and the direction of the asymmetry is the same so that the fiber has differential frictional effect.

FIG. 1 shows the outer layer of the fi'ber of the present invention,

FIGS. 2 and 3 are scanning type electron microscopic photographs showing the surface condition of a fiber of the present invention,

FIG. 4 shows the relationship between pull-out resistance and pull-out distance of a fiber out of the fiber bundle,

FIG. 5 shows the relationship between the interval of the protuberances on the fiber surface the hand of knitted fabric converted from the fiber.

Height, shape and interval of the protuberances are.

calculated from the secondary electron image obtained by positioning the fiber at right angles to the primary electron beam and taking the focus on both sides of the fiber (upper and lower parts in FIG. 2 or FIG. 3).

Differential frictional effect, as employed herein, means such characteristics as that when the frictional resistance, of a fiber pulled out of the fiber bundle from the tip to root direction (counter-direction) of the serration on the fiber surface is higher than the frictional resistance when a fiber is pulled out of the fiber bundle the root to tip direction (co-direction) of the serration on the fiber surface. Detailed explanation of a method for measuring the differential frictional effect is given in the Journal of the Textile Institute, vol. 37, T 269 (1946).

Height of the protuberances is more than 0.2;. and preferably from 0.3 to 1.0a. When the height is lower than 0.2 hand feel of the fiber product is not improved.

Interval of the protuberances is in a range of from 1.5 to 13,u, preferably from 1.5 to 12,11. and most desirably from 2.5 to 7 1..

FIG. 5 shows the relationship between interval of the protuberances and hand feel of knitted fabric obtained by spinning fibers having of about 0.6 height at an interval of from 1 to 12p and having no differential frictional efiect into a doubled yarn of 40 counts and knitting the yarn into a plain knitting yarn of 12 gauge.

Evaluation of hand feel was performed by many people skilled in such evaluation of fabric and classified into five grades, assuming that hand feel of cashmere wool is grade 5 (best) and that of the conventional acrylonitrile polymer fiber having no protuberances is grade 1.

From FIG. 5, it is understood that when the interval of the protuberances is from 1.5 to 12, hand feel of the fabric is improved, while, when the interval becomes 1 effect of the protuberances is markedly decreased and hand feel of the fabric resembles a fabric from fibers having no protuberances. Especially interesting is that the interval of the protuberances to give the best hand feel to the fabric is about 3 and this interval is far smaller compared with that of 6 to 12 for W001 fiber.

In the present invention, fiber having differential frictional effect has protuberances whose cross-section along the fiber axis is asymmetrical and the direction of the asymmetry is in accord with the direction in which the fiber is stretched in the manufacturing step.

Frictional resistance of pulling such fiber out of the fiber bundle in the co-direction (arrow direction as shown in FIG. 3) was measured at various pull out distances to obtain such a curve as shown in FIG. 4. Maximum pull-out resistance in FIG. 4 is defined as co-directional puli-out resistance (T Separately, frictional resistance when pulling a fiber out of the fiber bundle in the counter-direction (opposite direction to the arrow shown in FIG. 3) was measured at various pull-out distances, and the maximum pull out resistance is defined as counter-directional pull out resistance (T The ratio of T2/ T is a measure of the differential frictional effect. In the present invention the ratio of T T is preferably 1.3 to 3.5. The higher the protuberance the lower the preferable ratio. A fiber having differential frictional effect has a more improved hand feeling than a fiber having no such effect.

Acrylonitrile polymer fibers of the present invention are produced by treating acrylonitrile polymer fibers with a denaturalizing agent (as hereinafter defined) and then immersing the treated fibers into a shrinking agent. In more detail, an acrylonitrile homopolymer or acrylonitrile copolymer of more than 85 weight percent of acrylonitrile with a copolymerizable monomer, for example, methyl acrylate, methyl methacrylate, vinyl acetate, vinyl chloride, vinylidene chloride and vinyl bromide is spun by a wet-, dry-, dry and wet-, semi meltor gel-spinning method. Conjugate spinning methods may also be used.

The acrylonitrile copolymer may contain a copolym erizable basic monomer such as acrylamide or vinyl pyridine, or an acidic monomer such as sodium vinyl benzene sulfonate, sodium p-sulfophenyl methallyl ether or sodium methallyl sulfonate for improvement of dyeability.

The fibers are then washed with water and stretched to orient the molecules. The stretched fibers may be heat treated in a slack or tensioned state. The fibers are treated with a denaturalizing agent. Denaturalizing agent, as employed herein means a chemical agent for making the outer layer of the fiber insoluble in dirnethyl formamide at 75 C. and for making the structure of the outer layer different from that of the inner layer of the fiber. The fibers treated with the denaturalizing agent are then immersed into a heating medium or solvent for use as a. shrinking agent to shrink them.

The reason for the formation of the protuberances is an acrylonitrile polymer fiber is successively changed in its structure from its outer layer toward its inner (center) layer by the treatment with the denaturalizing agent, whereby the chemically and physically changed outer layer is formed. When the fibers are subjected to rapid heat treatment by immersing the fibers into an inert heating medium at high temperature or the fibers are subjected to heat treatment by immersing the fibers into a heated solution containing a solvent the acrylonitrile polymer, the inner layer is shrunk more than the outer layer.

Height and interval of the rotuberances are adjusted by controlling conditions for the denaturalizing and shrinking treatment. Whether the cross-section of the protuberances is symmetrical or not and whether the fiber has differential frictional effect or not depends on the conditions of the shrinking treatment.

According to the present invention, it is possible to easily form the protuberances of more than 0.2/4. at an interval in a range of l to 13 on the fiber surface.

The denaturalizing treatment is preferably performed by treating the fibers with an aqueous solution of alkali metal hydroxides, alkaline earth metal hydroxides, sulfuric acid, chloric acid, nitric acid, hydrazine or hydroxylamine salts. In the denaturalizing treatment, the structure of the fibers is successively changed from the outer layer toward the inner layer (center). The denaturalizing agent to be used is not restricted to the aqueous solutions above described.

it is n c s y s make the area if e ou e y r les than 40%, preferably less than 30%, of the cross-sectional area to form sulficient protuberances.

When the fibers are discoloured by the denaturalizing treatment, the fibers may be bleached with acid or a conventional bleaching agent.

The shrinking treatment is performed by rapidly heating the fibers with an inert heating medium or immersing the fibers into a glycol solution of organic carbonate or 'y-butyrolactone, which is a solvent for acrylonitrile polymer, and then heating the fibers.

For rapid heating, any such method is used as immersing the fibers into an inert high temperature liquid, heating the fibers with steam or superheated steam or contacting the fibers with heated metal such as a roller or plate, e.g. when the fibers are in a filamentary state.

As the inert liquid, a glycol such as ethylene glycol, propylene glycol, diethylene glycol, glycerine or polyethylene glycol, melted metals a, hydrotropic agent such as urea or thiourea or a concentrated aqueous solution of the hydrotropic agent is used. In short, as a rapid heating method, a method is used capable of rapidly heating (for example in one minute) the fibers to a desired temperature of above C., whereby the fibers are shrunk more than 5%.

To be emphasized here, is the effect of rapid heating (shock heating). In any example described hereinafter, if the fibers were subjected to the denaturalizing agent and when the fibers were gradually heated to shrink about the same extent, protuberances are not developed at all or protuberances are only slightly developed. Protuberances of more than 0.2 height in the present invention are developed by only rapidly heating the fibers.

As the glycol solution of organic carbonate or y-butyrolactone, ethylene glycol, diethylene glycol, glycerine or polyethylene glycol containing less than 30% of ethylene carbonate, propylene carbonate, trimethylene carbonate, tetramethylene carbonate or 'y-butyrolactone is used.

The fibers treated with the denaturalizing agent are immersed into the glycol solution of organic carbonate or 'ybutyrolactone and then heated in the solution to above 70 C. to shrink the fibers more than 5%. The heating may be carried out after Withdrawing the fibers out of the solution and squeezing the fibers to such an extent that solution adhered to the fibers is less than 300% based on the Weight of the fiber.

Fibers having differential frictional effect also produce by immersing the fibers treated with denaturalizing agent into an aqueous solution containing less than 30% of organic carbonate such as ethylene carbonate, propylene carbonate, trimethylene carbonate, tetramethylene carbonate, or 'y-butyrolactone (solvent for the acrylonitrile polymer) and heating the fibers in the solution to above 70 C. to shrink the fibers more than 5%. Heating may be carried out after withdrawing the fibers out of the solution and squeezing the fibers to such an extent that the solution adhered to the fibers is less than 200% based on the weight of the fiber.

The aqueous organic carbonate or 'y-butyrolactone solution may contain a neutral salt, preferably the sulfate of the alkali metals, alkaline earth metals, manganese, aluminium or ammonium. By adding these salts to the aqueone solution, it is possible to lower the concentration of the organic carbonate or -butyrolactone. For example, by adding sodium sulfate, it is possible to lower said concentratlon to one third. The aqueous solution may also contain a softening agent for conventional acrylonitrile polymer fiber. By adding the softening agent, it is possible to omit a separate softening treatment. This method is elfective when the shrinking treatment is performed on a yarn or knitted or woven fabric. By this method, a hand feel of the fabric comprising the present fibers and conventional acrylonitrile polymer fibers is prevented from deteriorating due to mutual adhesion of the conventional fibers in the shrinking treatment.

The heat shrinking treatment may be p rformed u er substantially no tension or low tension and the heat shrinking treatment may be performed in any state such as tow, staple, spun yarn or fabric. Further, similar protuberances can be developed by carrying out the denaturalizing treatment and the heat shrinking treatment in separate steps, for instance, by denaturalizing the fibers in a tow state, spinning the tow into yarn and then heat shrinking the yarn.

Another object of the present invention is to provide a process for preparing a fiber product of markedly high commercial value. That is, the fiber of the present invention by its protuberances gives the final product a soft, wool-like oily and highly resilient hand feel similar to that of wool fiber of good quality. Since the protuberances supress the displacement of fiber in the fiber product and the protuberances of the present fiber have no such sharp edges as occur in Wool the product has an excellent antipilling property, which is one defect of wool products.

Further, in one embodiment of the present invention, it is possible to cause acrylonitrile polymer fiber, having primary aflinity to cation dyes, to be acid dyeable.

The fiber of the present invention having these characteristics is very desirable for mix spinning, union (mix) twisting, union (mix) knitting, union (mix) weaving with Shrinkage (percent) other known kinds of fibers, such as wool, cotton, rayon. other acrylonitrile polymer fiber, polyester fiber and polyamide fiber. For example, it is possible to increase the anti-pilling property of wool without spoiling the excellent hand feel thereof by mix spinning of the present fiber and wool. It is possible to obtain a product of exceedingly high commercial value and of a multi-colour effect by mix spinning the present fiber with wool since the present fiber is dyeable with cation dye and conversely, wool is dyeable with acid dye.

EXAMPLE 1 Acrylonitrile copolymer containing 92% acrylonitrile and 8% vinyl acetate was dissolved in dimethyl acetamide to prepare a spinning solution of 28% polymer concentration. The spinning solution was extruded through a spinneret into a coagulating bath containing 50% dimethyl acetamide and 50% water and kept at 40 C. in order to form filaments. The resultant filaments were stretched 4.5 times in boiling water, washed with water, dried at 140 C. and then heat treated with steam of 2.5 kg./cm. in a slack state.

The tow thus obtained had a mono-filamentary denier of 3 and total denier of 60,000. The tow was immersed into a 2.0% aqueous sodium hydroxide solution kept at 90 C. for minutes to saponify the outer layer of the fiber and then bleached with a 2% aqueous oxalic acid solution at 98 C. for 15 minutes.

Fibers of the tow were treated with an embedding substance comprising parafiin and ethyl cellulose and cut into a piece of 4, thickness. The cut piece was immersed into dimethyl formamide to be partially dissolved.

FIG. 1 shows a photograph of the scanning type electron microscope (Type JSM II, made by Japan Electron Optics Laboratory Co., Ltd.) where the obtained cut piece remained insoluble. From FIG. 1 is is noted that an insoluble part of 1 thickness was formed on the fiber surface.

Such an insoluble part is not formed on a fiber not subjected to the aqueous sodium hydroxide solution.

In this example, ratio of the outer layer area to the cross-sectional area of the fiber was 21%.

The tow treated with the aqueous sodium hydroxide solution was continuously shrunk in a glycol bath shown in Table 1 to a predetermined extent by controlling the 6 tension applied, Washed with water and then subjected to a finishing treatment.

FIG. 2 shows the surface condition of the resultant fiber. From FIG. 2 it is seen that tucklike protuberances, the edge line of which is at an angle of from 75 to to the fiber axis, were discontinuously formed around the fiber surface.

Interval and height of the protuberances varied with the shrinking condition as shown in Table 1.

As referential examples, fibers not subjected to the treatment with sodium hydroxide solution were shrunk without development of the protuberances.

TABLE 1 Protuberance 1 5 Shrinking bath Shrink- Intertemp. age, val Height No Shrinking agent 0.) percent (a) Ethylene glycol 180 25 5. 1. 0 do 180 18 6. 0 0. 5 200 37 3. 0 1. 0 200 20 5. 5 0 7 180 25 6. 4 0. 8 6 ..dc 180 18 9.4 0.4 7 Propylene glycol 180 15 10. 1 0.3 8 Polyethylene glycoL 180 15 9.5 0. 4

Fiber length before shrmkmg-Fiber length after shrinking X 100 Fiber length before shrinking TABLE 2 Anti- Comprcspilling sional property Hand resilience (grade) (grade) Fabric from the fibers of No. 3 in table 1 s5. 3 4-5 3. s Fabrlc from the conventional fibers... 79.5 3-4 1. 0

NorE.-Op1npressional resilience: Measured in accordance with J IS L-1005. Anti-pining property: Classified based on the change of appearance generated on the surface of the fabric after operating with a random tumble-type tester (made by Atlas Electric Device 00.) in accordance with J IS L-l01S-1962 (the higher the grade, the better the antipilling). Hand feel: Classified and based upon sensory tests by many people skilled in evaluation of hand fecl assuming that hand feel of a product from fibers not treated in accordance with the present invention is grade 1 and hand of a merino wool product is grade 5.

EXAMPLE 2 An acrylonitrile polymer fiber tow produced by the same method as in Example 1 was treated with a 57% aqueous sulfuric acid solution kept at 80 C. for 10 minutes, washed with water and then dried.

The resultant fibers had an outer layer which was insoluble in dimethyl formamide as in Example 1. Ratio of tlgeqouter layer area to the fiber cross-sectional area was 1 0.

The tow was then immersed into urea as a hydrotropic agent or melted metal (composition, Bi; 50%, Pb; 24%, Sn; 14%, Cd; 12%) at C. to shrink. It was observed that protuberances, the edge lines of which were at about a right angle to the fiber axis, were formed on the fiber surface.

EXAMPLE 3 Example 1 was repeated, except that the heat shrinking conditions shown in Table 3 were used. It was observed that the protuberances were formed on the fiber surface at about a right angle to the fiber axis.

TAB LE 3 Shrinking conditions Tempera- Time Shrinking agent (part by weight) ture 0.) (mm) Ethylene carbonate/ethylene glycol (25/75) 100 15 Ethylene earhonate/glyeerine (20/80) 100 30 Propylene carbonate/ethylene glycol (25, 75) 100 10 EXAMPLE 4 Example 1 was repeated, except that the heat shrinking conditions as shown in Table 4 were used. Surface condition of the obtained fiber is shown in FIG. 3. As noticed from FIG. 3, protuberances formed on the fiber surface were quite different from those in Example 3, more precisely; a cross'section of the protuberances along the fiber axis was asymmetrical across the center line of the protuberances and the direction of asymmetry of the cross-section was uniform. Height and interval of the protuberances having an asymmetrical cross-section were varied with the shrinking conditions.

In FIG. 2 and FIG. 3, the direction of the arrows is that of extrusion of the spinning solution in the manufacturing step of the fiber.

As a referential example, fibers coated with a substance insoluble in dimethyl formamide were shrunk under the conditions as shown in Table 4 to form protuberances having no differential frictional effect. Therefore, it was concluded that the formation of protuberances having an asymmetrical cross-section is related to the history of deformation of fiber in its manufacturing step.

Tow obtained by the present example was filled into a ditch of 5 x 5 x cm., a weight load of 33 g./crn. was applied and pull-out resistance of the fiber from the fiber tow was measured at a pull-out rate of 160 cm./min. Frictional force, which is the maximum pull-out resistance in the co-direction or counter-direction of the protuberances, is shown in Table 4. It is not surprising that protuberances having such differential frictional effect were not developed on the fibers having no outer layer even by the heat shrinking treatment.

bonate/rnanganese sulfate! water (7/59/34).

Fibers obtained by the present example had protuberances, a cross-section along the fiber axis was asymmertical and direction of the asymmetry was uniform.

The fibers were soften and more'wool-like and oily than the fibers in Example 1 and the obtained fabric from the fibers of the present example had a hand feel of grade 4.2.

EXAMPLE 5 An acrylonitrile polymer fiber tow produced by the same method as in Example 1 was treated with an aqueous solution of denaturalizing agent as shown in Table 5 to make the outer layer of the fiber insoluble in dimethyl formamide. Ratio of the outer layer area to the fiber cross-sectional area is also shown in Table 5.

The tow was then treated in a heat shrinking bath of ethylene carbonate/Water (20/80) at C. for 30 minutes. By this treatment, protuberances having diflerential frictional effect were formed on the fiber surface.

TABLE 5 Denaturalizing conditions Ratio Concenof the tration of Temperenter the agent ature Time layer Denaturalizing agent (percent) 0.) (min) area Sodium hydroxide 1. 5 30 17 Potassium hydroxide 3.0 95 30 13 Lithium hydroxide 15 95 30 15 EXAMPLE 6 Acrylonitrile copolymer containing 92.5% of acrylonitrile, 7% of methyl acrylate and 0.5% of sodium sulfophenyl methallyl ether was dissolved in dimethyl acetamide to prepare a spinning solution.

This spinning solution was extruded into a coagulation bath to form filaments, stretched, washed, dried and heat treated with steam by the same method as in Exampie 1. t

The fibers obtained were cut into staples of m./rn. average length, treated in a bath containing 13% O.W.F. of hydroxylamine sulfate and 20% O.W.F. of sodium phosphoric acid and of 1:7 bath ratio at C. for 90 minutes, washed with water and dried. The resultant fibers had an outer layer hich was insoluble in dimethyl formamide as in Example 1. Ratio of the outer layer area to the fiber cross-sectional area was 29% The fibers were then treated with a 20% aqueous solution of ethylene carbonate at 95 C. for 30 minutes to shrink the fibers. The obtained fibers had protuberances having differential frictional effect on the fiber surface as in Table 4.

The obtained fibers had an affinity to acid dye. The fibers of the present example were mix spun with the fibers of No. 11 in Table 4 at a ratio of 25/75 into doubled yam of 2/36 MC (250/360 T/M), knitted into plain knitting of 14 gauge and dyed under the following conditions:

The obtained dyed fabric had a multicolour effect of yellow of acid dye and light brown of the cation dye, and the fabric was of a very high commercial value due to its being very soft, oily and resilient.

Colour fastness of the dyed fabric was excellent according to 118 (Japanese Industrial Standard) as shown in Table 6.

As a referential example, fibers treated with only hydroxylamine sulfate and conventional acr'ylonitrile polymer fibers were mix spun and the resultant yarn was dyed under the same conditions as in the present example. Properties of the Obtained fabric are also shown in Table 6.

TABLE 6 Colour fastness (class) MC-2 l MG-2 2 Fast- Dis- Dis- Fastness to Compres- Antiness colourcolourrubbing 3 sional pilling Hand to ation, atlon, resilproperty feeling light fading Talnt fading Taint Dry Wet ience 4 (grade) (grade) Dyed fabric of the present example 5-6 5 4-5 5 4-5 4-5 4 89. 4 45 4. 4 Dyed fabric of the referential example 5-6 5 4-5 5 4-5 4-5 4 30. 6 3-4 1. 5

Based on JIS Ll0451959. 3 Based on JIS 114046-1959.

EXAMPLE 7 Acrylonitrile copolymer containing 95% of acrylonitrile and 5% of acrylamide was dissolved in dimethyl acetamide to prepare a spinning solution.

This spinning solution was extruded into a coagulating bath to form filaments, stretched, washed, dried and heat treated with steam by the same method as in Example 1.

The fibers obtained were cut into staples of 100 m./m. average length, treated in a bath containing 20% O.W.F. of hydrazine sulfate and of a bath ratio of 1:7 at 100 C. for 90 minutes, washed with water and dried, the resultant fibers had an outer layer insoluble in dimethyl formamide as in Example 1. Ratio of the outer layer area to the fiber cross-sectional area was 16% The fibers were then treated in a bath containing 8 parts by weight of ethylene carbonate, 42 parts by weight of sodium sulfate and 50 parts by weight of water at 98 C. for 30 minutes to shrink the fibers. The obtained fibers had protuberances having differential frictional effects on the fiber surface.

EXAMPLE 8 Conventional acrylonitrile polymer fibers of 100 m./m. average length and of 3 denier (produced by Mitsubishi Rayon Co., Ltd.) were spun into plied yarn of 36 MC (250/360 T/M) by conventional worsted spinning. The obtained yarn was treated in a 2% aqueous sodium hydroxide solution kept at 90 C. for 30 minutes and bleached with a 2% aqueous oxalic acid solution at 98 C. for minutes. Ratio of the outer layer area to the fiber cross-sectional area was 21% The yarn was then immersed into a 7% aqueous ethylene carbonate solution kept at 40 C. for 10 minutes, withdrawn from the solution, squeezed to such an extent that the solution adhered to the yarn was 70 weight percent of the yarn and then dried at 100 C. for 60 minutes in a drier using heated air.

The cross-section along the fiber axis of the protuberances formed on the surface of the obtained fibers was asymmetrical and direction of the asymmetry was uniform.

EXAMPLE 9 Conventional acrylonitrile polymer fibers obtained in Example 8 were treated in a bath containing 13% O.W.F. of hydroxylamine sulfate and O.W.F. of sodium phosphate and of 1:7 bath ratio at 120 C. for 90 minutes, washed with water and dried. The resultant fibers had an outer layer which was insoluble in dimethyl formamide as in Example 1. Ratio of the outer layer area to the .fiber cross-sectional area was The fibers were mix spun with conventional acrylonitrile polymer fibers of 3 denier at a ratio of 40:60 into plied yarn of 36 MC (250/360 T/M) and the obtained yarn was dyed under the following conditions:

3 Based on .1 IS L-10481959. Based on J IS L-1005.

The dyed yarn was then immersed into a suspension comprising 8% ethylene carbonate, 7% softening agent (Zontes TA; trademark of a softening agent made by Matsumoto Oil and Fats Company, Ltd.) and water kept at 40 C. for 10 minutes, squeezed to such an extent that the suspension adhered to the yarn was 7 weight percent of the yarn and dried at C. for 60 minutes in a drier using heated air.

By this treatment, protuberances having differential frictional effect were formed on the surface of the obtained fibers as shown in Table 4.

The yarn was knitted into plain knitting of 14 gauge. Dyed knitted fabric thus obtained had multicolour effect of yellow with acid dye and light brown with cation dye, and was of a very high commercial value due to its being very soft, oily and resilient.

EXAMPLE 10 Acrylonitrile copolymer (A component) containing 95 of acrylonitrile and 5% of vinyl acetate and acrylonitrile copolymer (B component) containing 91.5% of acrylonitrile and 8.5% vinyl acetate were dissolved in dimethyl acetamide to give spinning solutions each having a 23.5% polymer concentration, respectively. Both spinning solutions were extruded simultaneously through common side by side orifices at a ratio of 1:1 into an aqueous coagulating bath containing 60% dimethyl acetamide at 30 C. to form conjugate filaments, stretched 5.0 times in boiling water, dried at C. at a constant length and then beat relaxed in saturated steam of 2.0 -kg./cm. to shrink about 20%, whereby crimps were developed.

The obtained conjugate fibers of 3 denier (mono-filamentary denier) were cut into staples of 100 m./m. average length, treated with a 2% aqueous sodium hydroxide solution kept at 90 C. for 30 minutes and bleached with a 3% aqueous acetic acid solution at 90 C. for 30 minutes. The resultant fibers were then thrown into a glycerine bath preheated to C. to rapidly shrink the fibers. By this treatment protuberances, the edge line of each being at about a right angle to the fiber axis, were formed on the fiber surface.

The obtained fibers were mix spun with merino wool at a ratio of 80:20 into plied yarn of 36 MC (/320 T/M) and knitted into fabric. The obtained fabric was very soft, oily and resilient.

What we claim is:

1. An acrylonitrile polymer fiber containing more than 85 by weight of acrylonitrile having a saponified outer layer insoluble in dimethyl formamide at 75 C. of less than 40% of the cross-sectional area thereof and having protuberances of a height in the range of 0.2 to 1.0,u at

an interval in the range of 1.5 to 12g on the surface of said fiber said protuberances resembling a tuck running discontinuously around said fiber and the edge line of said protuberances being at an angle of 75 to 105 to said fiber axis.

2. The acrylonitrile polymer fiber of claim 1, wherein a cross-section of said protuberances along the fiber axis is asymmetrical across the center line of said protuberances and said fiber has a differential frictional efiect.

3. A process for producing an improved acrylonitrile polymer fiber consising essentially of immersing an acrylonitrile polymer fiber containing more than 85% by weight of acrylonitrile into an aqueous solution of a denaturalizing agent selected from the group consisting of sodium hydroxide, potassium hydroxide, lithium hydroxide, sulfuric acid, hydroxylamine sulfate and hydrazine sulfate, to saponify and make the outer layer of less than 40% of the cross-sectional area of said fiber insoluble in dimethyl formamide at 75 C., and then immersing said treated fiber into a shrinking agent selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, polyethylene glycol, glycerine, urea, thiourea and inert melted metal and maintained at a temperature higher than about 130 C. to rapidly shrink said treated fiber more than the resultant fiber having protuberances of a height in the range of 0.2 to 1.0 1 at an interval in the range of 1.5 to 12 on the surface of said fiber, said protuberances resembling a tuck running discontinuously around said fiber and the edge line of said protuberances being at an angle of 75 to 105 to said fiber axis.

4. A process for producing an improved acrylonitrile polymer fiber consisting essentially of immersing an acrylonitrile polymer fiber containing more than 85 by weight of acrylonitrile into an aqueous solution of a denaturalizing agent selected from the group consisting of sodium hydroxide, potassium hydroxide, lithium hydroxide, sulfuric acid, hydroxylamine sulfate and hydrazine sulfate to saponify and make the outer layer of less than 40% of the cross-sectional area of said fiber insoluble in dmethylformamide at 75 C., and then immersing said treated fiber into a solution of a shrinking agent selected from the group consisting of ethylene carbonate, propylene carbonate, trimethylene carbonate, tetramethylene carbonate and -y-butyrolactone and maintained at a temperature higher than about 70 C. to shrink said treated fiber more than 5%, the resultant fiber having protuberances of a height in the range of 0.2 to 1.0a at an interval in the range of 1.5 to 12 on the surface of said fiber, said protuberances resembling a tuck running discontinuously around said fiber and the edge line of said protuberances being at an angle of 75 to 105 to said fiber axis.

5. The process of claim 4 wherein said solution of said shrinking agent is an aqueous solution.

6. The process of claim 5 wherein said aqueous solution also contains a sulfate selected from the group consisting of sodium sulfate, potassium sulfate, magnesium sulfate and zinc sulfate.

7. The process of claim 4 wherein said solution of said shrinking agent is a glycol solution.

8. A process for producing an improved acrylonitrile polymer fiber consisting essentially of immersing an acrylonitrile polymer fiber containing more than 85 by weight of acrylonitrile into an aqueous solution of a denaturalizing agent selected from the group consisting of sodium hydroxide, potassium hydroxide, lithium hydroxide, sulfuric acid, hydroxylamine sulfate and hydrazine sulfate to saponify and make the outer layer of less than 40% of the cross-sectional area of said acrylonitrile polymer fiber insoluble in dimethyl formamide at 75 C., immersing said treated fiber into an aqueous solution of a shrinking agent selected from the group consisting of ethylene carbonate, propylene carbonate, trimethylene carbonate, tetramethylene carbonate and y-butyrolactone, withdrawing the fiber from said solution and squeezing said fiber whereby the amount of solution adhered thereto is less than 200% by weight of said fiber, and heating said fiber to a temperature higher than about C. to shrink said fiber more than 5%, the resultant fiber having protuberances of a height in the range of 0.2 to 1.0 1. at an interval in the range of 1.5 to 12 on the surface of said fiber, said protuberances resembling a tuck running discontinuously around said fiber and the edge line of said protuberances being at an angle of to 10-5 to said fiber axis.

References Cited UNITED STATES PATENTS 3,069,222 12/ 1962 Hermes 8-1 30.1 3,514,249 5/1970 Bullington 8l30.1 3,045,318 7/ i962 Kern 28-76 3,498,737 3/1970 Robinson 8-114.5 3,393,083 7/1968 Go 161180 X 3,423,284 1/1969 Marek et a1. 161-180 X LEON D. ROSDOL, Primary Examiner H. WOLMAN, Assistant Examiner U.S. Cl. X.R.

8-l30.l, 177 R, 177 AB; 161-180, 181 

